Systematic correspondence in co-evolving languages

Language co-evolution is an influential cultural force, impacting the past, present, and future of human languages. Systematic correspondence identifies corresponding features in languages evolving together, such as English "d" and German "t" in word pairs like “deed–Tat” and “deep–tief”. This study examines how social ecology influences lexical-phonological systematic correspondence using a vector-based measurement—weighted cosine systematicity—across two co-evolutionary lexical datasets for comparison: old to recent English-German related words, and thirty-year sliced morphemic transcriptions for Chinese dialects in Shanghai. Results show that even when related but socially independent languages evolve in different directions, they can maintain an equilibrium in systematic correspondence over centuries. In contrast, dialects can rapidly converge towards their national high variety in terms of lexical-phonological similarities, and the regional standard in terms of systematic correspondence within decades. This suggests that self-regulation of cross-linguistic systematic correspondence has its own, yet complementary, mechanism compared to the similarity-based co-evolutionary mechanism, making it a meaningful indicator and predictor for cross-linguistic lexical co-evolution.